JPH03242367A - Novel casting/slip composition and manufacture of ceramics - Google Patents

Abstract

PURPOSE: To obtain a slip compsn. useful for a good ceramic casting compsn. by compounding an inorg. granular material, an org. solvent or vehicle and a specific dispersant.

CONSTITUTION: This slip compsn. contains the mixture composed of the inorg. granular material, the org. solvent or the vehicle and the dispersant to the above-mentioned granular material expressed by formula I. In the formula I, R₁, R₂, R₃ are each a linear or branched hydrocarbon chain or alkylaryl, an R group not exceeding 1 is CH₃ and the remaining R groups have respectively at least 6 to 30 carbon atom lengths; Y is (CH₂)_n (n is 1 to 10) and formula II (m is 1 to 5); X denotes COO^-, SO₃ ^-1, PO₃ ^-2. The examples of the inorg. granular material to be used include aluminum oxide, silicon carbide, tungsten- cobalt carbide, etc., and the preferable grain size thereof is 0.01 to 20 μm.

COPYRIGHT: (C)1991,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION This invention relates to improvements in ceramic slip and tape casting compositions. Specifically, the present invention is directed to ceramic casting compositions using organic solvents.

More particularly, the present invention is directed to the use of certain types of dispersants for inorganic casting compositions.

The following factors must be tested to determine whether a good casting composition has been formed: particle size; settling rate; sensitivity to mold conditions; peelability; shrinkage during drying; Pouring speed; No bubbles; Finally, low evaporation rate of the vehicle. Characteristics of a good casting composition are: (1) the slip should flow easily, fill all mold details, and should not exhibit significant yield points or significant dilatancy or thixotropy; (2) particles in the casting composition; should not settle to the bottom too quickly, otherwise the casting composition or casting product will have tapered walls and a thick bottom and the final fired ceramic part will have an excessive number of flaws or defects; (3) The casting composition must be flexible and easily release from the mold, and should not shrink to an excessive amount during drying; (4) The strength of the cast object prior to firing may be affected by handling, trimming, or Must be sufficient to allow further shaping;
(5) The casting speed when using the composition must be compatible with reasonable production rates and good properties;
(6) the casting composition should not produce excessive amounts of foam that would result in the entrainment of air bubbles in the pre-fired casting; and (
7) The solvent used in the casting composition should have a relatively low evaporation rate so as not to form a dry film on the exposed surfaces of the casting composition.

Typically, conventional casting compositions containing organic solvents used natural or synthetic polymers or copolymers as dispersants. Examples of these types of substances include fish oil;
Cross-linked fatty acid triglycerides, corn oil, unsaturated fatty acid glycerides, and Lubriz
LB2155 (polyisobutenyl succinimide) manufactured by OL Corp). Although all of these materials yield suitable organic casting compositions, there is room for substantial improvement. It is an object of this invention to provide improved casting or slip compositions using unique dispersants.

SUMMARY OF THE INVENTION The basic object of the invention is to provide a casting composition suitable for use in molding or tape casting.

A further object of the invention is to provide a molding method using the casting composition of the invention.

Other objects and advantages of the invention will be set forth in part in the following description, and in part will be obvious from the description, or may be learned by practice of the invention.

The objects and advantages of the invention may be realized and achieved by means of the instrumentalities and combinations particularly pointed out in the claims.

To achieve the foregoing objects, and in accordance with the objects of the invention encompassed herein and broadly described, the present casting composition comprises a powdered inorganic material, an organic solvent or vehicle, and the following two: [wherein R+, Rz, R1 are linear or branched hydrocarbon chains and alkylaryl, and not more than one R group is CH,
and the remaining R groups are each at least 6 to 30 carbon atoms long; Y is (CHI), (where n=1 to 10) and (-CHz-CH-CHz)m (In the formula, m=1~
X is selected from the group consisting of COO-, SO3-, P(h'');

As broadly described and encompassed herein, in another aspect of the invention, the method comprises mixing an inorganic powder material with an organic solvent in the presence of a dispersant having the formula to form a casting composition. forming the ceramic article by applying the casting composition to a suitable substrate, drying the casting composition for a sufficient time to remove the organic solvent, and firing the dried composition to form a finished ceramic product. Including.

The casting compositions and methods of the present invention provide ceramic articles with increased density and compaction compared to prior art ceramic articles. Furthermore, the casting compositions of the present invention are substantially not sensitive to water, at least within the operating range normally associated with methods using the casting compositions.

That is, the casting composition provides good dispersion of the inorganic particulate material even in the presence of water in the composition or starting materials. In the past, typical organic casting compositions were unacceptable because water immediately caused flocculation and/or precipitation of dispersed organic particles and loss of favorable rheology (ie, flow characteristics). Although the dispersants of the present invention are not highly water soluble, they provide organic dispersion casting compositions with relatively high moisture tolerance. For example, casting compositions prepared with the dispersants of the present invention were able to tolerate up to 20% water by weight without adverse effects on the composition. This means that the casting compositions of the present invention can tolerate water as an impurity and that no special handling is required during casting operations.

The presently preferred embodiments of the invention will now be described in detail.

The casting composition of the present invention comprises an inorganic particulate material, an organic solvent or vehicle, and the following structure: R2-"N-Y-X3c, where R+, Rz, R1 are linear or branched hydrocarbons. chain or alkylaryl, and not more than one R group is CH3
and the remaining R groups are each at least 6 to 30 carbon atoms in length; Y is (CH,), , (where n-1 to 10) and (-CH2-CH-C )lz)m (where m=1~
X is selected from the group consisting of COO-, 503-, POz''. Useful in forming electronic ceramics.

Inorganic particulate materials suitable for use in the casting compositions of the present invention can include common ceramic or inorganic materials. Typical examples of suitable inorganic particulate materials useful in ceramic applications include metal oxides such as aluminum oxide, magnesium oxide, calcium oxide, zirconium oxide, etc.; intermetallic compounds such as silicon carbide, titanium carbide,
Titanium nitride, aluminum nitride, zirconium carbide, etc.; Cermets such as tungsten carbide-cobalt;
Metallics such as tungsten and molybdenum and slip casting fluorides such as calcium fluoride. The inorganic particulate material should be compatible with the organic solvent used to form the casting composition. Typically the weight percent of inorganic particulate material is about 5-80%
, preferably from 5 to 50%, particularly preferably from 5 to 40%.

However, it is to be understood that these ranges are exemplary only, and it is envisioned that outside of these ranges, particularly low amounts of particulate material, may be suitable for the practice of the present invention.

The size of the particles making up the solid phase can vary widely depending on the density of the inorganic material and the desired properties of the fired article. but,
Particles should be within the colloidal size range. Dense materials require submicron particles to avoid settling. My experience is that the oxide object that is fired and vitrified has a diameter of 20 mm.
It should consist of submicrometer particles, with at least half of the particles being between 1 and 5 micrometers.

Very fine particles, such as particles less than 1 micrometer, can create problems because they require large amounts of liquid to provide useful slip to the casting composition. Preferred particle sizes for inorganic particles in the practice of this invention are 0.01 to 20 microns, most preferably 0.
．． It is 5 to 10 microns.

Organic solvents used to suspend inorganic particles in casting compositions have relatively low vapor pressures, are compatible with suspended particulate matter, are inexpensive, have low viscosities, and have the ability to dissolve dispersants. should have. Typical organic solvents for the casting compositions of the present invention include acetone, ethyl alcohol, benzene, butanol, methanol, isopropanol, methyl isobutyl ketone, toluene, trichloroethylene and xylene. The organic solvent used in a preferred embodiment of the invention is toluene.

The dispersants of the present invention are generally classified as zwitterionic and must have the formula shown above. This zwitterionic dispersant has been shown to provide casting compositions that are tightly packed and yield green unfired ceramic compositions with high density.

Another advantage is that the dispersant controls the settling time of the casting solution. Finally, the zwitterionic dispersants of the present invention provide casting compositions with high tolerance to impurities such as water. The dispersants of this invention are low molecular weight monomers consisting of polar head groups containing at least one positive and one negative charge in the branched hydrocarbon tail. Unlike previously known polymeric dispersants, they do not contain repeating functional units, giving casting dispersions that, upon settling, give a product with high density resulting in a ceramic with high material properties, giving a good casting composition. . A specific example of a dispersant suitable for the present invention includes H (C+o)J''(Me)CHz-COO-.

Weight percent of dispersant on solids is 0.5-10%
, preferably within the range of 1 to 8%. Most preferably the range is 2-5%.

It should, of course, be understood that the particularly preferred weight percentage of dispersant in the casting composition will depend on the end use of the resulting cast product and can be determined by routine experimentation by one skilled in the art.

Optionally, conventional binders and antifoam agents can be added to the casting compositions of the present invention. Typically these types of binders include polyvinyl alcohol, urea formaldehyde, carboxymethyl cellulose, ethyl silicate, and the like. Typical antifoam agents include small amounts of octyl alcohol.

The casting compositions of the present invention are suitable for conventional molding or casting operations. It is envisioned that it will find important application in doctor blading processes for shaping ceramic materials. Typically, the doctor blading process involves suspending a finely divided inorganic powder in a non-aqueous liquid system containing an organic solvent, a binder, and a dispersant to form a slurry that is cast onto a moving carrier surface. The slurry is leveled or "
pass under the knife or blade to 'doctor'. As the solvent evaporates, the fine solid particles coalesce into a relatively dense flexible sheet that can be stored on a take-up reel or peeled from the carrier in a continuous array. "Tape method"
, "knife coating", "tape casting"
and the term "sheet casting" has been used interchangeably with doctor plating in reference to the process of forming thin, relatively large area sheets of ceramic compositions.

This specific method has been established as a useful manufacturing method for various electronic ceramics. Typical applications include capacitors, piezoelectric elements, ferrite memories, electrically insulating substrates for thick and thin film circuitry, and substrates for catalysts.

It is generally advantageous for the production of relatively large area, thin but uniform sheets with high unfired density. The typical range and fired thickness of parts made by this method is 0.001 to 0.045 inches. Complex shaped parts with complex hole patterns can be formed directly by punching or stamping parts from cast sheets.

The average particle size of the inorganic powder in the casting composition is about 0.
It is 4 micrometers. The particle range is 0.1-3 micrometers. Typical organic solvents used are alcohols and toluene.

In fact, the method can be used with common materials such as Teflon (Tefl).
on), Mylar, cellophane and cellulose acetate. The carrier film is selected to provide a clean, smooth, impermeable, insoluble surface.

It should not adhere too tightly to the carrier as the dry slip will cause difficulty in peeling the tape (ie the dry slip) from the carrier.

However, the slurry should have sufficient adhesion or interaction with the carrier during drying to effectively control shrinkage during drying, causing it to occur in the thickness direction substantially perpendicular to the tape carrier. It has been suggested that plasticizers be added to the slurry composition to avoid excessive stickiness of the slurry to the tape. However, these materials do not form part of the invention and are readily selected by those skilled in the art.

In a preferred embodiment of the method of the invention, inorganic particulate material,
A casting composition/slip containing an organic solvent and a dispersant having the above formula is mixed in a vessel. The slurry is then transferred from the container to a carrier sheet that passes under a doctor blade. The doctor blade levels the casting composition on the sheet as it passes by. Evaporation of the organic solvent in the slurry leaves a pre-fired green ceramic coating on the carrier sheet. The resulting dry pre-fired ceramic is then heated to a high temperature (i.e. 5
00°C or higher) to produce a finished ceramic product.

The following examples are presented as illustrations of preferred embodiments of the invention.

Example materials Colloidal SiC, particle size in the micron range - Colloidal AlN1 Particle size in the micron range - Toluene for reagents - Corn oil, fish oil, LB-2155 [manufactured by Lubrizol] - 2T-1", 2 of the present invention
T-271), IT-3TI'' dispersant - 10cc graduated cylinder, acid washed and oven dried - No. 00 black rubber stopper, acetone washed and air dried.

General Simulation The casting or slip compositions tested in each of the following specific examples were prepared as follows.

A well-prepared dispersant (e.g. CaC+ oN” (1,le) CHzOHCH[:
H2SO3-) was dissolved in toluene 7 in a cleaned cylinder.
Dissolved in cc. The cylinder was pre-acid cleaned to remove traces of organic matter and detergent that could interfere with dispersion testing.

Exactly 0,0005 g of colloidal inorganic powder are dropped into the solution in quick small additions. Cap the cylinder and record the total volume of solids and liquid.

The fixed initial volume is also recorded if visible. The cylinder is shaken vigorously by hand for 2 minutes and then allowed to settle undisturbed at room temperature. The rate of settling is recorded by measuring the level of the solid/liquid interface as a function of time.

In poorly dispersed systems this rate is very fast and difficult to measure in the first minute as a result of solids sticking to the glass walls. In a well-dispersed system, the sedimentation rate is slow;
Often confirmed by smooth column fall of non-adhesive solids. The final sediment volume is the value measured after the solid-liquid interface has reached a stable level. In poorly dispersed systems this level of stability is achieved within 2-3 hours with minimal change for 2-12 hours.

It is observed that in highly dispersed systems this level continues to become compact for up to 12 hours.

Example 1: Sedimentation rate of SiC in toluene In this experiment, three “ZTJs” used in the practice of the invention containing different head groups and/or made by different operations
The dispersant is tested at 1% by weight/SiC against a blank control and two city version dispersants, fish oil and LB-2155. The results are shown in FIG. The first time is Si during time.
It is a graph plotting the sedimentation rate of C. As shown in this figure, the rZTJ dispersant can be used for a very short time (2 minutes of shaking) as evidenced by the slow settling rate.
- form a highly dispersed slurry. The trend after 30 minutes is due to a more compact ceramic from the rZTJ dispersant.

SiCゞ　　　　　　　9 Data regarding stable sediment volume are recorded in Table 1.

Lower SiC volumes were achieved for all dispersants compared to untreated controls. 2 Among commercially available dispersants, LB-21
55 was slightly better.

All 3 rZTJ dispersants produced dense sediments that were much harder than the control and commercial dispersants. This indicates the formation of a highly ordered sediment microstructure that reduces defects in the finished fired ceramic.

Table 1 1. Blank Control 2.14 2. Fish Oil 1.90 3. LB-21551,56 - Not Uniform Loose Sediment Granular Sediment 2, (Fish Oil) and 3. (LB-2155) is SiC
There are two commercially available dispersants reported to be effective against.

4. 2T-1” is the structure (cs) (CIO) N
(Me) has -CH2-CH-CH3SO4.
OH5, ZT-2τN has the structure (C,o)zN(Me)-CIZ-Coo-.

6,2T-3'' has the same structure as ZT-2, but was isolated from a different reaction type.

All separation agents were weight Si in 7.0 cc toluene solution.
C was tested at 1.0% by weight.

Example 2: Sedimentation rate of Ai'N in toluene
), the efficacy of rZTJ dispersants used in the practice of the present invention was compared. Similar to Example 1, r used in the present invention
The ZTj dispersant showed excellent performance as shown in the graph shown in FIG.

The final sediment volume of AIN in toluene was recorded for various dispersants and is shown in Table 2. Again, denser and more orderly sediments were obtained with the rZTj dispersant used in this invention than with the blank control, fish oil, and corn oil.

Table 1, Blank Control 2.65 - Unlike Loose Sediment 2, Fish Oil 2.62 - Unlike Loose Sediment 3, Fish Oil 1.20 - Unlike Loose Sediment Headings 2.3 and 4 is a commercially available dispersant used in ceramic processing.

Headings 5.6 and 7 are zwitterionic rZTJ compounds having the structures shown in Table 1. Headings 4-7 are in very close range since the experimental close range in measuring small volumes (less than lcc) is ±0.1 cc.

All dispersants were tested at 1.0% by weight Ai'H in a solution of 7.0 cc toluene.

Example 3: Effect of rZTJ dispersant concentration on sedimentation ZT
-1'' was tested at three dose levels based on weight percent SiC solids. Samples were prepared by essentially the same general procedure described above. The observed trend is towards slightly improved performance with increasing dose.

The following examples are presented to illustrate the ability of the casting compositions to withstand the presence of water as an impurity.

Example 4 Three samples were prepared by the following procedure. Control sample is 0.5g
It was prepared by mixing 7 cc of SiC in toluene without a dispersant. A second sample was prepared similarly to the control, but with the addition of 2% by weight LB-2155. A third sample was prepared similarly to the control using a dispersant designated as Formula % Formula % ITM. For each pre-dispersed sample, H2O2μ
Two aliquot portions were added and the dispersion was agitated for approximately 2 minutes. Sedimentation velocity and final sediment volume were recorded. The procedure was repeated increasing the addition of FI20 to 100 pJ.

Figures 4a and 4b graphically illustrate the results of this experiment.

Figure 4a plots the change in volume of each sample versus time. The results show that flocculation produced faster sedimentation rates in the control and LB-2155 samples compared to the casting composition of the present invention. FIG. 4b shows by a bar graph that the final settling volume of the inorganic particles dispersed in the casting composition of the present invention is about 1 cc compared to 2 or 3 cc for known commercial products which produce insufficiently low density compacts. show. These results indicate that the casting composition of the present invention maintained smooth settling velocity and high density compaction.

Example 5 This experiment was directed to a comparison of the settling rate and compaction volume of a casting composition of the present invention compared to a blank control using a mixture of inorganic particulate materials.

The casting composition was prepared according to the general procedure outlined previously but contained 0.25 g of SiC and 0.25 g of A.
jN was used. The results obtained are shown in the graphs shown in FIGS. 5 and 6. The graph dramatically demonstrated the effect that dispersant ZT-1'' had on the settling time (ie, a highly dispersed slurry resulting in a slow settling time) and final compact volume (more compact ceramic) for the casting composition.

The foregoing description has been provided for purposes of illustration and explanation.

It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teachings. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application. It is intended that the scope of the invention be defined by the claims.

[Brief explanation of drawings]

The drawings are incorporated in and form a part of the specification, illustrate aspects of the invention, and together with the description serve to provide a detailed explanation of the invention. 1 to 6 in the drawings are graphs showing the results obtained by implementing the claimed invention. FIG. Sedimentation rate of SiC in toluene FIG, 2 Sedimentation rate of AIN in toluene Time (min) - square time (min) → FIG, 3 Sedimentation rate vs. "ZTJa degree rZT of SiC in toluene" - 1 Dispersion time (min) )−+ FIG 0 FIG, 4b

Claims (9)

[Claims] (1) Inorganic particulate material, organic solvent or vehicle, and the following structure: ▲Mathematical formula, chemical formula, table, etc.▼ (In the formula, R_1, R_2, R_3 are linear or branched hydrocarbon chains or alkylaryl; , no more than one R group is CH_3, and the remaining R groups are each at least 6 to 3
0 carbon atoms long; Y is (CH_2)_n (in the formula, n = 1 to 10) and ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (in the formula, m = 1 to 5) selected from the group consisting of;
is selected from the group consisting of COO^-, SO_3^-, PO_3^-. 2. The composition of claim 1, wherein the inorganic particulate material is present at about 5 to 80 weight percent. 3. The composition of claim 2, wherein the dispersant is present at about 0.5 to 5.0 weight percent. (4) The composition according to claim (1), wherein the organic solvent is selected from the group consisting of methanol, ethanol, and toluene. 5. The composition of claim 1, wherein the inorganic particulate material comprises a mixture of at least two different particulate materials. (6) Claim (5) wherein the mixture contains AlN and SiC.
). (7) A method of manufacturing a finished ceramic article, comprising (a) an inorganic particulate material, an organic solvent or vehicle, and the following structure: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [wherein R_1, R_2, R_3 are linear or branched hydrocarbon chain or alkylaryl, not more than one R group is CH_3 and the remaining R groups are each at least 6 to 30 carbon atoms in length; Y is (CH_2 )_n (in the formula, n = 1 to 10) and ▲ mathematical formulas, chemical formulas, tables, etc. ▼ (in the formula, m = 1 to 5);
X is selected from the group consisting of COO^-, SO_3^-, PO_3^■; drying to remove the organic solvent to produce a dry unfired ceramic film on the substrate; (c) firing the dry film at an elevated temperature to produce a finished ceramic article. (8) The method according to claim (7), wherein the substrate is a carrier film. 9. The method of claim 8, wherein the slip composition applied to the carrier film is leveled with a doctor blade before drying to produce a thin film.